It was found that spectrin preparation brought about polymerization of the G-actin in a medium of relatively low ionic strength and this action of spectrin resides at the oligomer fraction. Since Ca ions was found to cause the superprecipitation of spectrin and actin, an investigation will be made into the effect of Ca ions on the G-actin polymerization property of oligomer. For this purpose oligomer will be prepared from old blood cell according to the methods of Pinder, et. al., (FEBS Letters. Vol. 104, 396, 1979) and the effect of Ca ions on polymerization of G-actin induced by oligomer will be investigated under various experimental conditions. Also the Ca ions binding to the actin in the presence of oligomers will be analyzed in the media containing different amounts of mono- and di-valent ions.